In the rolling bearing contact industry there is currently a tendency to integrate sealing devices between the non-rotating race and the rotating race of the bearing with a magnetised encoder wheel which forms part of a device for measuring the relative rotation speed between the bearing races.
The accompanying drawings 1 and 2 show an example of such a well-known technique. A rolling contact bearing, comprised of a non-rotating outer race 10, a rotating inner race 11 and two series of rotating elements 12, in this case spheres, is provided with a pair of sealing devices, indicated overall with the number 14, arranged on both sides of the bearing to hermetically close the space between the races 10 and 11. A metallic annular insert 15, firmly force fitted onto the non-rotating outer race 10, bears an annular sealing covering 16 which forms a pair of lips 17, 18, which slide against a metallic annular insert 19 onto which is vulcanised an annular rubber element 20; the rubberised insert 19 is then forcefully fitted onto the inner rotating race 11 of the bearing. The rotating insert 19 has a substantially L-shaped axial section, in which there is a cylindrical wall 21, which the lip 17 (defined here as radial) slides against and a radial wall in the form of a disc 22, which the lip 18 (defined here as axial) slides against.
The part 20a of the rubber element 20 which covers the axially outer side 22b of the disc-shaped wall 22 is charged with metallic particles to form an encoder wheel which, when it rotates, generates impulses of a frequency proportional to the rotation speed of the rotating race 11 in a fixed sensor facing said encoder wheel, which is not illustrated here for the sake of simplicity.
In order to assemble the two inserts 15, 19 with their respective rubber units 16, 20 onto the bearing in a single driving operation in which these two coupled units are forcefully thrust in an axial direction, it is indispensable that the two inserts with their relative rubber elements are reciprocally positioned in the correct fashion, according to the arrangement illustrated in FIG. 2.
Given the particular arrangement of the sealing lips of the watertight shield, the coupling between the two units derives solely from the radial thrust which the radial lip 17 exerts against the wall 21, while the axial thrust exerted by axial lip 18 against the axially inner surface 22a of the wall 22 tends to separate the two units.
It is not easy to obtain this state in practice, due to other factors which tend to separate the two units, such as for example shock or impact sustained during transport.
In case one or both of the sealing covering lips should slip from their operating position which is set during the pre-assembly step, there is a risk that the sealing device of the bearing could be assembled in an incorrect arrangement in which the lips 17, 18 do not come into contact with the respective walls 21, 22. This results in the malfunction of the sealing device and thus shortens the working life of the bearing due to insufficient sealing action.